Light valves have been used for more than fifty eight years for modulation of light. A light valve may be described as a cell formed of two walls that are spaced apart by a small distance, at least one wall being transparent, the walls having electrodes thereon usually in the form of transparent, electrically conductive coatings. Between the cell walls of the cell is a "light valve suspension", which may be a liquid having a plurality of small particles suspended therein. See, for example, U.S. Pat. No. 4,407,565. Alternatively, the "light valve suspension" may be in the form of a film having droplets of a liquid light valve suspension distributed in the film, the liquid light valve suspension comprising a plurality of small particles suspended in a liquid suspending medium. See, for example, U.S. Pat. No. 4,919,521. In such cases, the film is located between the opposed cell walls.
In the absence of an applied electrical field, the particles in the light valve suspension exhibit random Brownian movement, and hence a beam of light passing into the cell is reflected, transmitted or absorbed, depending upon the nature and concentration of the particles and the energy content of the light. When an electric field is applied through the light valve suspension in the light valve, the particles become aligned and for many suspensions most of the light can pass through the cell.
Light valves have been proposed for many purposes including, e.g., alphanumeric displays, television displays, windows, mirrors, filters, ski goggles, eyeglasses and the like to control the amount of light passing therethrough.